Laser devices for coherent optical communication

Coherent detection techniques, which have been used in radio communication for decades, are now starting to be used in optical communication systems. With coherent detection, a tenfold improvement in receiver sensitivity and a dramatic improvement in selectivity can be achieved. This paper describes requirements and performance of laser devices used in coherent optical communication systems. Ultra-narrow linewidth 1.5 µm external cavity semiconductor lasers have been used both as transmitters and as local oscillators in coherent systems, and as pump lasers in Fiber-Brillouin Amplifiers. Semiconductor laser amplifiers (SCLA) have been used as in-line and pre-amplifiers in both direct and coherent detection communication systems.